SEMINAR: OzROMS – a three dimensional continental shelf and slope model for Australia

The regional ocean modelling system, ROMS—a three-dimensional numerical model with a high spatial resolution (~2–4 km), developed for the continental shelf and slope regions of Australia—is presented. This is the first time a model of this nature with all the relevant forcing (tides, winds, air–sea exchange, density) has been included in a single model for Australian waters running over annual time scales. The model was developed to quantify shelf–ocean fluxes of water and carbon and therefore also includes a coupled biogeochemistry module. The OzROMS model, which covers the whole Australian region, consists of 30 sigma layers in the vertical, and is forced with three-hourly meteorology data (wind, atmospheric pressure, heat and freshwater fluxes) derived from ECMWF ERA interim data. The model’s open boundary tracers (salinity and temperature) and transport (barotropic and three-dimensional velocity components) are specified using the global Hybrid Coordinate Ocean Model (HyCOM) output. The model’s open boundary forcing included tides derived from the TPX07.2 global tidal model and monthly climatological mean sea levels derived from the AVISO database. Various data sources were used to validate the model, with majority of the data derived from IMOS data sets obtained from moorings, ocean gliders, HF radar, satellite imagery and coastal tide gauges. The high skill levels suggest the model is capable of accurately simulating the whole spectrum of time scales, from semidiurnal to annual scales.
In this presentation, we will take you on a tour of all the major physical processes and circulation patterns around Australia, all of which were reproduced by OzROMS. These processes include major surface and subsurface current systems (e.g. the Leeuwin current, Leeuwin undercurrent, Flinders current and East Australian current) and their associated eddies. The model also reproduce seasonal current systems (e.g. the Holloway, Ningaloo, and Capes currents in WA); physical processes, such as summer upwelling (e.g. at Ningaloo, Shark Bay, Capes, and Bonnie); dense shelf water formation and cascading off the south-western Australian shelf; internal wave generation along the North West Shelf; and, inertial oscillations at the critical latitude. Considering sea levels, the model captured both tidal amplitudes and phase variations around the Australian coast including resonance amplification of tides in Bass Strait, Broad Sound (Queensland) and along the North West Shelf; and, continental shelf waves generation from tropical cyclones and frontal systems. The coupling of the hydrodynamic model with biogeochemistry is briefly described, and initial estimates of the shelf–ocean water exchanges along the WA and SA shelves are presented.